We investigated if monthly gadolinium (Gd)-enhanced magnetic resonance imaging (MRI) can assist the clinician in anticipating the diagnosis of multiple sclerosis (MS) in the very first few months following a clinically isolated syndrome (CIS). A consecutive series of CIS patients with > or = 3 T2-weighted (T2W) hyperintense brain MRI lesions suggestive of MS were followed up for the first six consecutive months after enrollment with monthly triple-dose Gd-enhanced brain MRI scan. MRI conversion to MS was defined by the presence of either > or = 1 new Gd-enhancing lesion or > or = 1 new T2W lesions in the subsequent MRI scan. Sixty patients were included. Of them, 30 (50%) had at least one Gd-enhancing lesion on the baseline MRI scan. After three months, MRI conversion to MS was observed in 80% and 62% of patients based on the appearance of > or = 1 new T2 lesion and > or = 1 new Gd-enhancing lesions, respectively. The presence of > or = 1 new T2W lesion was observed in 90% and 82% of patients who had, at baseline, a Gd-positive MRI scan and dissemination in space based on the new McDonald's criteria, respectively The rate of MRI conversion remained almost stable in the last two MRI scans. Our study suggests that the majority of CIS patients with an abnormal baseline scan showed an MRI conversion to MS after three months. The model of six months as the optimal interval for repeating MRI exam is not supported by the present data.